Two studies (each reviewing a number of other studies) and an article putting it in lay terms:

"He and others have estimated that for every two pounds of weight you lose, your metabolism slows by about 25 calories per day, and your appetite increases by about 95 calories per day. So in other words, if you lose 20 pounds, your body will burn roughly 250 calories less each day while craving about 950 calories more.

To maintain your weight loss through dieting over time, you’ll have to continue eating less while resisting a rising appetite and slower metabolism, which is “increasingly difficult,” Dr. Schur said.

The drive to eat more is so strong because our brains “sense that our energy stores are being depleted,” she added, and “that’s a threat to our survival.”"

So diets mostly all work in the short term, but people just return to their top weight over time. Your body is always trying to get you back to your top weight.

https://pubmed.ncbi.nlm.nih.gov/32238384/

https://onlinelibrary.wiley.com/doi/abs/10.1111/obr.12949

https://www.nytimes.com/2024/01/11/well/eat/dieting-weight-loss.html